1. Field of the Invention
The present invention relates generally to filtration systems and devices, and more specifically to an air filtering device which is removably attachable to a conventional portable electric fan. The present device essentially comprises a filtering element which fits against the back of the fan guard, with a generally toroidally shaped shroud attaching to the periphery of the fan guard at the rear of the fan to guide air past the motor and through the filter.
2. Description of the Related Art
In recent years, people have become more aware of various airborne impurities which are commonly found in indoor environments in the home, office, and other locations. Such impurities range from secondhand tobacco smoke to asbestos dust and other less hazardous materials. Many such hazards, such as those two noted specifically above, are considered to be sufficiently dangerous that indoor smoking has been banned in most areas of the country and considerable sums of money have been spent on asbestos cleanup.
Nonetheless, other undesirable airborne impurities in the form of dust, pollen, etc., generally circulate in most indoor environments, even with centralized filtration systems associated with conventional central heating and air conditioning systems. Accordingly, various systems and devices have been developed in the past in attempts to filter or clean the ambient air within a relatively small localized area, such as a room or individual office space. These devices and systems have generally not provided the efficiency and economy desired in such devices, for various reasons noted further below.
Accordingly, a need will be seen for a filtering device for attaching to the back of a conventional portable electric fan, for guiding air through the back of the fan and for filtering air as it passes through the fan guard to be expelled from the front of the fan. The present air filtering device generally comprises a toroidally shaped solid shroud which may be removably attached to the back of the fan guard to surround the motor. An annulus is defined between the inner edge of the shroud and the motor, to guide airflow past the motor and through the back of the fan guard. A toroidal filter secures about the motor and between the fan guard and shroud, with all air passing through the fan being required to pass through the filter. The filter may be formed of durable material for cleaning and reuse, or may be disposable, as desired.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 2,883,790 issued on Apr. 28, 1959 to Reed J. Blackman, titled xe2x80x9cFan-Type Insect Catching Device,xe2x80x9d describes an assembly comprising a screen installed at the outlet side of the fan, with an electric light bulb installed at the inlet side of the fan. The Blackman device is intended to capture insects by means of attracting insects to the light, whereupon they are drawn into the fan and captured by the screen extending from the outlet side. Blackman teaches away from the present invention, as he cannot install the capture screen on the inlet side as it would at least partially conceal the insect attracting light source which of course must be placed at the inlet side of the fan. Moreover, the screen used by Blackman is relatively coarse in comparison with the filtering material of the present invention, as even the smallest insect is many orders of magnitude larger than the particulate matter which is captured by the present filter.
U.S. Pat. No. 4,477,272 issued on Oct. 16, 1984 to Craig E. Hollis et al., titled xe2x80x9cFan Filter,xe2x80x9d describes a filter disc which is removably secured to the back of the fan guard of a conventional portable fan. Hollis notes the benefit of placing the filter upstream of the fan to reduce or preclude the buildup of foreign matter on the fan blades, which is a widely recognized problem. Yet, the Hollis et al. filter does not completely cover the inlet side of the fan guard, due to a slot provided in the filter to fit the device over the fan motor in back of the guard. The present filter secures completely and tightly about the fan motor, thereby directing all airflow through the filter.
U.S. Pat. No. 4,750,863 issued on Jun. 14, 1988 to Glenn Scoggins, titled xe2x80x9cFan Shroud Filter,xe2x80x9d describes a filter and shroud for installation with a permanently installed ceiling fan, rather than a portable desktop or similar fan as provided with the present fan filter. Scoggins places his filter above the fan, to the inlet side of the fan when the fan is blowing downwardly. As no guard means is conventionally applied to such ceiling fans, the Scoggins filter would tend to be drawn into the fan, whereas the present filter is drawn against the back of the fan guard to help hold it securely in place. Moreover, the Scoggins shroud attaches to the ceiling above the fan or to the suspension shaft of the fan, as no guard is provided for attachment of his filter device.
U.S. Pat. No. 4,781,526 issued on Nov. 1, 1988 to Clarence Mead, titled xe2x80x9cFan And Filter Combination,xe2x80x9d describes a filter system for installation to a conventional xe2x80x9cbox fan,xe2x80x9d having a square shroud. The Mead filter device requires modification of the fan shroud by installing guide rails along each side thereof, for sliding the rectangular filter element therein. In contrast, the present filter system does not require any modification of the fan for its placement thereon. Moreover, Mead does not provide any form of close fitting shroud about the fan itself, as provided by the present invention. The Mead filter is more like a conventional central furnace or air conditioning filter, having a rigid structure and periphery, and is not adapted for installation to a tabletop fan or the like, where the flexibility of the present filter element allows it to conform to the back of the fan guard.
U.S. Pat. No. 4,889,543 issued on Dec. 26, 1989 to Jerry D. Burt, titled xe2x80x9cAir Filtering System,xe2x80x9d describes a rotating filter which is attached to the blades of a ceiling fan. The Burt filter is completely different from the present filtering system, in that (1) no shroud is provided, (2) the filter elements attach to the fan blades and thus rotate with the blades, rather than remaining stationary relative to the moving blades as in the present fan filter system, and (3) the filter elements do not closely envelop the fan motor in order to preclude entrainment of foreign matter through the center of the fan circulation. The Burt filter system can only be used on a relatively slowly turning, large diameter fan such as a ceiling fan, as the high speed of the typical table top fan would throw the filter elements from the blades due to centrifugal force.
U.S. Pat. No. 5,641,340 issued on Jun. 24, 1997 to Anton Kagan, titled xe2x80x9cMethod For Filtering Air In Laminar Flow,xe2x80x9d describes a first embodiment directed to filtering airflow through cooling fans as used in computers and the like. The only embodiment of the Kagan disclosure which is adaptable to portable fans, is shown in FIGS. 7 and 8 of the Kagan ""340 U.S. Patent. In those Figures, an annular ring shaped filter is secured to the outer perimeter of the generally circular fan guard. Kagan fails to provide any form of filter for the back of the fan, where incoming air is entrained through the fan blade path by the rotating blades. The present filtration system covers this entire area, to capture dust and other foreign matter before it enters the guard and blade path.
U.S. Pat. No. 5,904,744 issued on May 18, 1999 to Anton Kagan, titled xe2x80x9cFan Filter With Fasterning (sic) Means,xe2x80x9d describes further variations on the filtering methods of the ""340 U.S. Patent to the same inventor, discussed immediately above. The various embodiments of the ""744 Kagan U.S. Patent which are directed to smaller desktop and table type fans are all of essentially the same configuration as those of the ""340 U.S. Patent, i. e., the filter does not extend directly into the airflow path of the fan, either upstream or downstream of the blades. Rather, the Kagan filter is a circumferential device applied to the fan guard periphery, outside of the circular blade path. While this might reduce slightly any impurities ejected from the tips of the rotating blades, such air movement is a relatively small volume, of the total air moved by a fan or propeller, and would produce a relatively small filtering effect in comparison with the generally diametrically disposed filter of the present invention.
U.S. Pat. No. D-359,800 issued on Jun. 27, 1995 to James J. Cich, Jr. et al., titled xe2x80x9cAir filter For Attachment To A Fan Grill,xe2x80x9d illustrates a design for a fan filter having a semicircular configuration with an apparently rigid grate thereacross. The only means of securing the device to the fan guard is by a series of clips about the inner central arcuate edge of the device, rather than being held in place by a solid guard and secured about the fan motor at the back of the fan, as in the present filter. The Cich, Jr. et al. filter covers less than half of the rotating area of the fan, unlike the present filter which covers all of the fan area.
U.S. Pat. No. D-372,079 issued on Jul. 23, 1996 to Dennis M. Fago et al., titled xe2x80x9cFan Filter,xe2x80x9d illustrates a design for a filter having a circular shape with a rim extending therefrom. An opening is provided in the center of the disc area, with an apparently decorative trim strip extending around the opening and radially outwardly therefrom. No means for securing the device to a fan or indication of attachment to the front or back of the guard is apparent, nor is any form of solid shroud shown. Moreover, the Fago et al. design apparently comprises only a single thickness, rather than the double thickness provided by the present filter device.
U.S. Pat. No. D-408,513 issued on Apr. 20, 1999 to Dwayne E. Reede, titled xe2x80x9cFilter For A Round Fan,xe2x80x9d illustrates a design closely resembling that of the Fago et al. ""079 U.S. Design Patent, discussed immediately above. No means of securing the device to a fan is apparent, nor is any form of separate solid shroud disclosed in the ""079 Design Patent. It is also noted that as in the case of the Fago et al. ""079 design, that the Reede design comprises only a single thickness of material, unlike the double layers of filter material provided by the present invention, wherein one layer is drawn against the back of the fan guard while the opposite layer remains against the inside wall of the shroud, thereby defining a debris capture pocket between the two layers of filter material.
French Patent Publication No. 2,299,042 published on Oct. 1, 1976 describes (according to the English abstract) a centrifugal fan or blower having filters disposed to each side of the plane of rotation of the fan blades. Air is drawn in through the filters on each side, and expelled generally radially between the outer edges of the filter elements by centrifugal force. The ""042 French Patent Publication teaches away from the present invention, in that the shrouds or guards over the filters are required to be perforated in order to allow incoming airflow therethrough and through the filters to the centrally located centrifugal blower. The present shroud is solid and unbroken when installed on the fan, with the exception of the single passage through the center.
Finally, Japanese Patent Publication No. 3,302,234 published on Dec. 9, 1988 describes (according to the English abstract) a fan filter comprising a spiral wound corrugated belt. The filter configuration is thus somewhat similar to a conventional vehicle oil filter or the like, rather than comprising a porous woven or nonwoven material or open cell foam material, as in the case of conventional air filters. The filter of the Japanese Patent Publication is thus relatively deep and bulky, in comparison to the present filter. Moreover, no means of securing the filter to a conventional wire type fan guard is disclosed in the Japanese Patent Publication, as provided by the present filter invention.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.
The present invention is an air filter for use with a portable desktop or tabletop electric fan. The filtering device comprises a relatively thin, generally circular filter element captured between the back or inlet side of a conventional wire fan guard and a solid shroud. The filter element has a generally toroidal shape, resembling a tire, with the inner annular area being open for access to the interior of the device. A solid shroud is also provided, to capture the filter between the shroud and the back or inlet side of the conventional wire fan guard. One side of the filter is drawn against the back or inlet side of the fan guard when the fan is operating, with the opposite filter side lying adjacent to the inner surface of the shroud.
The shroud also has a generally toroidal shape when closed about the back of the fan guard, with hinge and/or clasp means for securing the two halves together about the fan guard. A series of clips are provided about the outer circumference of the shroud, for securing it to the periphery of the fan guard. The shroud includes a central opening therethrough which is larger than the motor casing of the fan, thereby defining an air inlet annulus for the fan. The outermost layer of the filter secures about a lip extending from the inner edge of the shroud, while the innermost layer of the filter secures about the fan motor housing, thereby precluding any leakage of unfiltered air past the filter. As the assembly secures only to the fan guard, it may be applied to both stationary and oscillating fans.
Accordingly, it is a principal object of the invention to provide an improved air filtering device for use with portable electric desktop and tabletop fans and the like.
It is another object of the invention to provide an improved, air filtering device, which device comprises a generally toroidally shaped filter element having first and second walls and an inner annular opening to the interior defined by the walls, and a solid shroud for capturing the filter element between the conventional rear or inlet side of the fan guard and the shroud.
It is a further object of the invention to provide an improved air filtering device wherein the filter element first wall is drawn against the rear side of the fan guard and the second wall rests against the inner surface of the shroud, with foreign matter being captured between the two walls of the filter element to clean the ambient air and reduce accumulation of foreign matter on the fan.
An additional object of the invention is to provide an improved air filtering device wherein the filter fits closely about the fan motor and secures tightly to the inner lip of the shroud, precluding passage of unfiltered air around the filter element.
It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.